Catheters, such as guiding catheters and catheter sheath introducers, used in angioplasty procedures are typically made from polymers such as polyurethane. It is often desirable that the distal tips of these catheters be radiopaque, so they are clearly visible under fluoroscope. This aids the physician in performing the angioplasty or other like procedure. An example of a prior art catheter having a radiopaque tip is found in U.S. Pat. No. 5,045,072 issued to Castillo et al. on Sep. 3, 1991, which is hereby incorporated herein by reference.
The distal tips of catheters are typically made of a polyether polyurethane formulation having a radiopaque filler such as bismuth trioxide. An example of one formulation contains 39.7 weight percent of a commercially available polyurethane (Pellethane 80AE, sold by the Dow Chemical Company); 60 weight percent of bismuth trioxide: and 0.3 weight percent of oxidized polyethylene, which is a commercially available and known dispersing agent, release agent, and lubricant for the system.
Recently, there has been a desire to make a catheter which has greater radiopacity than those now currently available. The more easily the physician can see the catheter tip under fluoroscope, the easier it is to perform the procedure and accurately locate the catheter within the body. However, when adding large amounts of radiopaque agents, such as bismuth trioxide, to polymers, the compound begins to degrade and lose many of the desired physical mechanical properties.
An example of an attempt to overcome the above difficulties and make a more radiopaque polymer distal tip for a catheter is given in U.S. Pat. No. 5,300,048 issued to Drewes et al. on Apr. 5, 1994, which is hereby incorporated herein by reference. This type a catheter uses a polymer, such as a polyether block amide. In order to make the composition more radiopaque, a compound having higher radiopacity per volume amount than bismuth trioxide was used. For example they used metal powders such as tungsten, platinum, gold, silver, lead and tantalum, in amounts greater than 75 weight percent and up to 95 weight percent. However, it has been found that in such a compound the radiopaque metal is not properly wetted and uniformly dispersed within the polymer, and in addition does not bond and seal well with the polymer. Therefore, it runs the risk of degrading and having particulates of radiopaque metal fall off. In addition, adding any of the known dispersing agents in this field, such as oxidized polyethylene, to such a compound does not effectively solve the problem. Those types of dispersing agents do not sufficiently bond and seal the metal within the polymer. Even with dispersing agents, some polymers, such as polyurethane, suffer a catalytic effect when large amounts of metals, especially bismuth compounds, are compounded with it.
Adding large amounts of metal powders to certain polymers can either cause them to degrade or not sufficiently bond to the polymer. Adding large amounts of other radiopaque agents, such as bismuth trioxide, does not work either. There has, therefore, been a need for a polymer compound which is more radiopaque than those described in the prior art. There has also been a need for such a compound wherein the radiopaque material is uniformly dispersed within the compound. There has also been a need for such a compound wherein the radiopaque material is bonded to and sealed with the polymer so that the risk of radiopaque particulate material becoming loose during the use of the product is minimized. The present invention is intended to fulfill such needs.